1. Technical Field of the Invention
The present invention relates to a mobile communication terminal having a plurality of antennas, such as a cellular phone or a personal digital assistant (PDA).
2. Related Art
Proposals have been made of a technology for stabilizing the antenna characteristic such as antenna gain or radiation efficiency irrespective of whether a terminal is held in a hand, put into a pocket, or the like (see, e.g., Japanese Unexamined Patent Application Publication No. 11-274966). The above publication describes the use of an embedded antenna in addition to a rod-like antenna in order to stabilize the antenna characteristic. Consequently, even when a user holds a mobile communication terminal in his/her left or right hand while transmitting speech by radio, the rod-like antenna and embedded antenna can be automatically switched based on a state of reception at a radio frequency.
When a plurality of antennas are included, the antennas may interact with each other. Consideration must therefore be taken into the arrangement of the antennas. In particular, when it comes to a folding type mobile communication terminal, the positional relationship between antennas varies depending on whether the terminal is closed (folded) or opened (unfolded). It therefore affects the antenna characteristic how a plurality of antennas are arranged. However, the related art does not reveal anything about a constituent feature suitable for a mobile communication terminal shaped to be able to be folded.
The prior mobile phones are configured such that a linear antenna comprising a whip antenna and an antenna top portion which incorporates a helical antenna as connected through an insulating spacer to the tip end of the whip antenna, is mounted in the casing. The pull-up of the top portion causes the whip antenna to be pulled out of the casing so as to receive phone radio waves through the whip antenna while the pull-in of the top portion causes the whip antenna to be stored in the casing, thereby enabling the helical antenna to be available for use in receiving the radio waves.
In order to keep the antenna characteristics as required for receiving phone radio waves through such linear antenna as mentioned above, the outline of the linear antenna, i.e. the size of the antenna top portion and the thickness and the length of the whip antenna, tends to be enlarged, suffering from difficulties in producing a more compact casing.
JP-A No. 36317/2001 discloses that the linear antenna and the surface mounting antenna are adjacently disposed, which linear antenna is excited by the power supplied to the power supply electrode of the surface mounting antenna. The mobile phone by concurrent use of two antennas as disclosed therein is simple in structure and provides enhanced antenna characteristics. Thus, the mobile phone can render its linear antenna smaller in size than the other prior mobile phones. However, because the linear antenna and the surface mounting antenna are adjacently disposed, upon storing the linear antenna as contracted into the casing, its top portion and casing portion to cover the surface mounting antenna might be wrapped by a user's hand, suffering from the deterioration of the antennas characteristics as required.